Questions & Answers about ظننت أنك في البيت.
Why does ظننت have two separate noon letters when its dictionary form ظنّ has a shadda?
ظن is a doubled verb, meaning its last two root letters are the same (ظ-ن-ن). For the 'he' form, they merge into ظنّ with a shadda. But when we add a past tense ending that starts with a consonant, like the 'I' ending ت, we must pull the two letters apart. That is why it becomes ظننت (Zanantu).
Why do we use أنك here instead of just saying 'that' and using the independent pronoun for 'you'?
In Arabic, the word for 'that' in the middle of a sentence is أن (anna). It acts like a magnet and requires the subject that follows it to attach directly as a pronoun suffix. So, أن + أنت (you) merges into أنك.
Why use أن (anna) instead of إن (inna)?
We use أن (anna) to connect clauses in the middle of a sentence, especially after verbs of thinking or feeling like ظننت. إن (inna) is mostly used at the absolute beginning of a sentence, or immediately after verbs of saying like قال.
Where is the word for 'were' in this sentence?
There isn't one! The second part of the sentence is an equational (verb-less) clause basically meaning 'you [are] in the house.' Because the main verb ظننت (I assumed) is in the past tense, it automatically shifts the context of the whole situation into the past.